In order to reduce the exposure of proton exchange membrane (PEM) fuel cells to problems resulting from freezing temperatures, and to reduce reliance on water pumps and other plumbing as accessories to the fuel cells, the total volume of coolant in the fuel cells may be reduced.
However, in systems which do not use either a coolant pump or a gas venting micropump, and have minimal external water plumbing, the flow rate of coolant or water in the cells is quite low. If only gas is vented from the coolant or water passageways, the flow is limited by the amount of water which evaporates into the reactant gases. With small passageways and low water flow, gas bubbles may join together (aggregate) and block water flow from large areas of the coolant channels which may cause porous, hydrophilic reactant gas flow field plates (water transport plates) to dehydrate. The dehydration allows gas to enter the coolant flow channels at too high a rate, sometimes referred to as “gas breakthrough” of the water transport plates, thereby causing localized heating and dehydration of the membrane at various spots, resulting in degradation of components and reduced performance.
Systems employing between-cell coolant plates, which have glycol or other coolants, are sometimes referred to as active water management (AWM) fuel cells, as disclosed in patent publication US 2005/0142408. AWM fuel cells may also have extremely small, in-cell water passageways to provide low flows of water to the anode side and/or cathode side of the fuel cells for water management, with insignificant cooling resulting from the water flow.